Former President Bill Clinton arrives at the U.S. Capitol for the ceremonial swearing-in of President Barack Obama during the 57th Presidential Inauguration in Washington, Monday, Jan. 21, 2013. (AP Photo/Cliff Owen)

Gallery: President Obama's second inauguration

Declaring “our work begins today”, President Barack Obama vowed to “finished what we started” four years ago as hundreds of thousands of inauguration-goers gathered on the historic National Mall in anticipation of his oath-taking for a second term.